Method of forming a thermoplastic cast by vacuum



Sept. 16, 1969 B. A. ADDISON ETAL 3,467,086

METHOD OF FORMING A THERMOPLASTIC CAST BY VACUUM Filed Nov. 14, 1966 INVENTORS BENJAMIN A. ADDiSON 'ERWIN R. JENNINGS THEODORE H. GEWECKE llg mw ATT'YS United States Patent M U.S. Cl. 128-90 1 Claim ABSTRACT OF THE DISCLOSURE A method of preparing a cast for a human limb employing a thermoplastic envelope about the limb, and heat-softening and vacuum-forming the thermoplastic envelope.

BACKGROUND AND SUMMARY OF INVENTION Conventionally, plaster of paris casts are employed. Not only are these heavy, but the preparation is a delicate, time-consuming matter. Both of these drawbacks are avoided by the instant invention and the provision of a cast and method of preparation which is lightweight and easily installed constitutes an important object of the invention.

Another object of the invention is to provide a cast which is made up of relatively rigid, thermoplastic material which can be vacuum-formed in situ.

Other objects and advantages of the invention may be seen in the details of structure and operation as set down in the following specification.

The invention is explained in conjunction with an illustrative embodiment in the accompanying drawing, in which FIG. 1 is a fragmentary perspective view of a human limb in the process of being equipped with the inventive cast;

FIG. 2 is a view similar to FIG. 1 but showing the limb in a subsequent stage of cast development;

FIG. 3 is a view similar to the preceding views but showing the cast in completed form;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3; and

FIG. 5 is a perspective view of a modified form of apparatus.

In the practice of the invention in conjunction with, for example, a broken arm 10, we provide an envelope generally designated 11, which can take the form of a pair of sheets 12 and 13, of thermoplastic material lightly united along adjoining longitudinal edges as at 14 and 15. Each of the sheets is perforated as at 16, and it will be appreciated that the material of which the sheets 12 and 13 is constructed is relatively rigid at normal temperatures, particularly 98 F.

In FIG. 2, the loose-fitting envelope 11 is seen to be enclosed with a flexible, stretchable enclosure generally designated at 17 and which is advantageously constructed of a material having a substantially higher melting or softening point than that reached during the course of the vacuum-forming to be described hereinafter. For example, the enclosure 17 may be constructed of silicone rubber, of a thickness so as to develop the conformability of the fashion seen in FIG. 3 upon the application of an internal vacuum. The enclosure 17 is equipped with a flow port as at 18 in which a tube 19 is connected. The tube, in turn, is coupled to a vacuum pump (not shown) adapted to collapse both the enclosure 17 and the envelope 11 after heat has been applied to the envelope 11.

Patented Sept. 16, 1969 A suitable source for heat for this purpose may take the form of infrared lamps as at 20, which deliver radiant heat to the envelope 11 to cause the same to change its shape to that designated 11 in FIGS. 3 and 4, and thus conform to the exterior shape of the arm 10.

The enclosure 17 is advantageously tubular and is constricted at its ends as at 21 and 22 and taped to provide a vacuum seal. The conduit 19 advantageously extends sufiiciently into the enclosure 17, as into the palm of the person whose arm is being equipped with a cast so as to prevent premature blockage of the conduit 19 by the flexible enclosure 17.

After the envelope 11 has been vacuum-formed, i.e., softened by heat and collapsed by virtue of atmospheric pressure, the enclosure 17 is removed and the projecting wings 23 (FIG. 4) are cut away, leaving a sturdy, yet lightweight, cast for the arm 10.

In one embodiment of the invention, we employ polyvinyl chloride sheeting to provide the envelope 11, the sheeting being perforated and having a thickness of the order of 0.050 inch to about 0.100 inch. With material of this character only limited heating is requiredfrom radiant sources for about one minute in duration so that the skin of the arm 10 is not blistered or burned. In this fashion, we achieve vacuum-forming in a range tolerable to humans, i.e., not substantially above the range 120-150 F.

By virtue of providing the perforate envelope 11, We avoid any discomfort that might be occasioned through the prevention of evaporation of perspiration. In some instances, it may be advantageous prior to enveloping the limb 10 to wrap the same lightly with gauze or light similar material.

In FIG. 5, a modified form of the invention is seen. There, the numeral designates generally a human arm which is positioned within an enclosure 111. The enclosure 111 is rigid having top and bottom hinged panels 121 and 122. Each panel is completed with two layers of plastic material-a perforated thermoplastic sheet 112 on the inside and a higher-melting stretchable sheet 117 on the outside. In the use of this arrangement, the panels are first heated by lamps 120 after which the panels are closed and vacuum-applied through the conduit 119. This causes the layers 112 and 117 to collapse into conforming relation to the arm 110.

We claim:

1. A method of preparing a cast for a limb comprising the steps of (1) placing a relatively rigid perforated thermoplastic envelope about a limb so as to enclose the limb within said envelope, (2) enclosing said envelope within a sealed enclosure, (3) heat softening said envelope to a moldable state, and (4) vacuum-forming said envelope to substantially the same configuration about said limb by application of a vacuum to said sealed enclosure, and (5) allowing the formed envelope to cool to a substantially rigid state, whereby the envelope immobilizes said limb.

References Cited UNITED STATES PATENTS 3,027,336 3/1962 Gotz et a1 12890 XR 3,286,693 11/1966 Clarke et a1 128-90 XR 3,314,419 4/1967 Quick 12890 3,329,143 7/1967 Gordon 12882 RICHARD A. GAUDET, Primary Examiner RONALD L. FRINKS, Assistant Examiner US. Cl. X.R. 264--92 

